Steel is a material having excellent physical properties for use in various industrial fields such as for vehicles, home appliances, and buildings. However, since steel reacts with oxygen and the like to easily cause corrosion, in order to prevent corrosion, surface treatment such as coating with a protective film is essentially required.
Steel is processed into various types such as a plate, a rod, and a tube, and among the types, a thin plate type of steel plate is a type of steel product most frequently used in the industrial fields. A method most frequently used to prevent corrosion of the steel plate is a method where a metal protective film having reactivity with oxygen which is higher than that of iron is applied on a surface of the steel plate to serve as a sacrificial anode and thus delay corrosion of the steel plate.
Representative metals of metals used when the steel plate is coated are zinc and aluminum, and examples of a method used to apply the metals on the steel plate include hot dipping, electroplating, and the like. A plating method is currently used in most steel plate surface treatment processes because a process thereof is easy and cost is low.
In the case where the steel plate is coated by using a zinc plating method, in order to improve corrosion resistance of the steel plate, a method of increasing a plating amount of zinc may be considered. However, a method of reducing a plating speed is used to increase the plating amount of zinc, but this method has a problem in that productivity is reduced.
Further, an increase in a plating amount of zinc is essentially accompanied by an increase in weight of the plated steel plate, which leads to a reduction in fuel consumption efficiency due to the increase in weight in the case of transporting machines. Moreover, currently, since natural resources of zinc are rapidly diminishing, it is urgent to discover a material capable of replacing zinc.
As a part of the aforementioned attempt, a method where a plating amount of zinc is not increased but heteroatoms are added to improve corrosion resistance of an existing zinc plated steel plate has been developed. Examples of the heteroatoms may include aluminum, magnesium, and the like.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.